Ghost busted: The frigid Boomerang Nebula reveals its true shape. The image is based on visible light observation, in blue, from the Hubble Space Telescope and short-wavelength radiation detected by the Atacama Large Millimeter/sub-millimeter Array in Chile.

Ghost busted: The frigid Boomerang Nebula reveals its true shape. The image is based on visible light observation, in blue, from the Hubble Space Telescope and short-wavelength radiation detected by the Atacama Large Millimeter/sub-millimeter Array in Chile. (Bill Saxton / National Radio Astronomy Observatory and Raghvendra Sahai, JPL)

Geoffrey Mohan

A new look at the coldest known object in the universe reveals a ghostly shape glowing in the Centaurus galaxy some 5,000 light years from Earth.

The Boomerang Nebula is a numbing 1 degree Kelvin, or about -458 Fahrenheit, more than a degree colder than the background radiation of the Big Bang, according to calculations by an astronomy team led by the Jet Propulsion Laboratory in La Cañada Flintridge.

Yet fringes of this pre-planetary nebula are warming, a phenomenon that may confirm a particle physics prediction made by Albert Einstein.

Images of the nebula were released Friday by the National Radio Astronomy Observatory.

A decade ago, observations from the Hubble Space Telescope showed a double-lobed shape to the nebula, which consists of a white dwarf star surrounded by the streams of high-speed gas it has emitted.

Dish telescopes that examine radiation in wavelengths of a millimeter or less, however, had suggested that the full shape of the nebula was more spherical. It took the recently constructed array of such dishes in Chile's Atacama Desert -- the Atacama Large Millimeter/sub-millimeter Array, known as ALMA -- to resolve the structure.

The double lobes in the visible light spectrum were confirmed, but calculations based on the array data revealed a more elongated expanse of gas. A band of dust around the star masks the visible light emissions, giving it the false hourglass image, according to the report, published in the Astrophysical Journal.

Even though the gases emitted by the dying star are cooling as they expand, the outer fringes of the nebula reveal a slight warming, the researchers noted. That phenomenon could be explained by matter that is absorbing light and emitting electrons, a photoelectric effect first proposed by Einstein, according to the authors.

The nebula data help astronomers understand the final stages of stars similar to our sun. In that sense, planetary nebula is a bit of a misnomer. These elderly stars have shed their outer layer and collapsed to a white dwarf, emitting ultraviolet radiation that gives the surrounding gas its characteristic glow. The dwarf of a pre-planetary nebula, however, is not quite at that stage, and its glow comes from light reflecting off star dust.